1. Field of Inventions
The present inventions relate generally to ambulatory infusion devices.
2. Description of the Related Art
Ambulatory infusion devices, such as implantable infusion devices and externally carried infusion devices, have been used to provide a patient with a medication or other substance (collectively “infusible substance”) and frequently include a reservoir and a pump. The reservoir is used to store the infusible substance and, in some instances, implantable infusion devices are provided with a fill port that allows the reservoir to be transcutaneously filled (and/or re-filled) with a hypodermic needle. The reservoir is coupled to the pump, which is in turn connected to an outlet port. A catheter, which has at least one outlet at the target body region, may be connected to the outlet port. As such, the infusible substance may be transferred from the reservoir to the target body region by way of the pump and catheter.
Ambulatory infusion devices frequently delivery the infusible substance in accordance with a continuous-delivery delivery profile that specifies one or more flow rates during the delivery profile cycle. Small volumes of infusible substance are delivered continuously. As used herein, “continuous” delivery means that (1) the fluid transfer device is actuated when fluid is scheduled to be delivered and (2) the fluid transfer device is physically capable of delivering the scheduled volume given its mechanical minimum. If, for example, a fluid transfer device is configured to deliver 0.25 microliter per actuation (partial actuations not being possible) and the continuous delivery profile calls for 0.25 microliter per minute, then continuous delivery would involve one actuation per minute. If, on the other hand, the same fluid transfer device was used in conjunction with a continuous delivery profile that called for 0.125 microliter per minute, then continuous delivery would involve one actuation every two minutes because the fluid transfer device is not capable of delivering 0.125 microliter. The continuous-delivery delivery profile is typically specified by a clinician and depends upon several factors including, but not limited to, the particular infusible substance formulation, the patient's condition, and the therapy being administered.
One issue that may, in some instances, be associated with the continuous delivery of an infusible substance is granuloma formation at the catheter outlet, especially in those instances where the patient is receiving a relatively high concentration of infusible substance over a relatively long period of time. A granuloma may partially or completely block the outlet, thereby preventing the patient from receiving the intended dosage of the infusible substance. Additionally, in the context of delivery to the intrathecal space, the formation of an inflammatory mass, or granuloma, may lead to spinal cord compression. One issue that may, in some instances, be associated with the delivery of small volumes of an infusible substance from a catheter into tissue is the failure of the infusible substance to disperse beyond the tissue that is close to the catheter outlet. Active protein drugs, such as neurotrophic factors, are examples of infusible substances that may have inadequate dispersion issues when delivered in small volumes from a catheter into tissue.